Digital still cameras including a solid-state image sensing device including a CCD or the like have become popular in recent years. FIG. 2 shows a configuration of an interline transfer solid-state image sensing device 1 used for a digital still camera. The solid-state image sensing device 1 forms an imaging area including a plurality of pixels 11 by having color filter arrays on a plurality of photo sensors arranged in the form of a matrix, and has a plurality of vertical registers 12 for transferring electric charges of a plurality of arrays of vertically arranged pixels 11, and a horizontal register 13 for outputting the electric charges transferred by these vertical registers 12 every one horizontal period.
The above solid-state image sensing device 1 has an input terminal 8 for a first vertical transfer pulse Vφ1 having a first phase, an input terminal 7 for a second vertical transfer pulse Vφ2 having a second phase, input terminals 6, 5 for a pair of third vertical transfer pulses Vφ3A and Vφ3B having a third phase, an input terminal 4 for a fourth vertical transfer pulse Vφ4 having a fourth phase, input terminals 3, 2 for a pair of fifth vertical transfer pulses Vφ5A and Vφ5B having a fifth phase, and an input terminal 1 for a sixth vertical transfer pulse Vφ6 having a sixth phase. Feeding these vertical transfer pulses to the respective input terminals causes electric charges accumulated in the vertical registers 12 to be transferred to the horizontal register 13.
The solid-state image sensing device 1 also has input terminals 21, 16 for a pair of first horizontal transfer pulses Hφ1A and Hφ1B, and input terminals 22, 17 for a pair of second horizontal transfer pulses Hφ2A and Hφ2B provided by inverting the first horizontal transfer pulses, respectively. Feeding these horizontal transfer pulses to the respective input terminals causes the electric charges transferred from the vertical registers 12 to the horizontal register 13 to be output outside.
The above solid-state image sensing device 1 is further provided with an input terminal 19 for a subpulse φSUB for causing an electronic shutter operation for sweeping out electric charges accumulated in the pixels before exposure of the imaging area.
A conventional digital still camera can set a monitor mode for displaying images (through images) photographed by the solid-state image sensing device 1 on a monitor every 1/30 seconds. FIG. 8 shows operations of the conventional digital still camera at a time when a shutter button is depressed with the monitor mode being set, and the vertical transfer pulses Vφ1-Vφ6, horizontal transfer pulses Hφ1A, Hφ1B, Hφ2A, Hφ2B, and subpulse φSUB to be fed to the solid-state image sensing device. SHT in FIG. 8 is a shutter pulse generated upon depression of the shutter button, and VD is a vertical synchronizing pulse. The vertical transfer pulses, horizontal transfer pulses and subpulse are a rectangular pulse. One block of the horizontal transfer pulses in FIG. 8 represents a series of horizontal transfer pulses.
As illustrated, the first vertical transfer pulse Vφ1, second vertical transfer pulse Vφ2, third vertical transfer pulses Vφ3A, Vφ3B, fourth vertical transfer pulse Vφ4, fifth vertical transfer pulses Vφ5A, Vφ5B and sixth vertical transfer pulse Vφ6 are fed continuously, and a series of the first horizontal transfer pulses Hφ1A, Hφ1B, and second horizontal transfer pulses Hφ2A, Hφ2B are fed intermittently to the solid-state image sensing device every one vertical period. This causes the electric charges accumulated in the pixels to be transferred as described later.
When the shutter button is depressed, in a first vertical period (#1V), a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed. Subsequently in a second vertical period (#2V), electric charges accumulated in the pixels due to the exposure in the first vertical period are transferred, and then, based on an image signal thereby obtained, a calculation for an exposure time and a focus adjustment value is started. In addition, a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed.
Next in a third vertical period (#3V), the calculation is continued, and thereafter the exposure time and focus adjustment value obtained by the calculation are set. In addition, electric charges accumulated in the pixels due to the exposure in the second vertical period are transferred, and then, based on an image signal thereby obtained, a calculation for an exposure time and a focus adjustment value is started. Further, a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed.
Subsequently in a fourth vertical period (#4V), the calculation is continued, and thereafter the exposure time and focus adjustment value obtained by the calculation are set. In addition, electric charges accumulated in the pixels due to the exposure in the third vertical period are transferred, and then, based on an image signal thereby obtained, a calculation for an exposure time and a focus adjustment value is started. Further, a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed. At this time, the exposure time and focus adjustment value set in the third vertical period will be reflected. Similarly, the following exposure, transfer, calculation and setting are concurrently performed during one vertical period.
When the shutter button is depressed, the above conventional digital still camera performs a series of photographing operations of an exposure, a transfer, calculation and setting over three vertical periods and every one vertical period as described above, and starts a photographing operation for image recording at a time point when an optimum exposure time and focus adjustment value are obtained.
The above conventional digital still camera has a calculation time exceeding one vertical period for obtaining photographing conditions such as an exposure time and a focus adjustment value. In contrast, FIG. 9 shows operations at a time when a shutter button is depressed of a conventional digital still camera with a calculation time less than one vertical period, and the vertical transfer pulses Vφ1-Vφ6, horizontal transfer pulses Hφ1A, Hφ1B, Hφ2A, Hφ2B, and subpulse φSUB to be fed to the solid-state image sensing device. SHT in FIG. 9 is a shutter pulse generated upon depression of the shutter button, and VD is a vertical synchronizing pulse. The vertical transfer pulses, horizontal transfer pulses and subpulse are a rectangular pulse. One block of the horizontal transfer pulses in FIG. 9 represents a series of horizontal transfer pulses.
As illustrated, the first vertical transfer pulse Vφ1, second vertical transfer pulse Vφ2, third vertical transfer pulses Vφ3A, Vφ3B, fourth vertical transfer pulse Vφ4, fifth vertical transfer pulses Vφ5A, Vφ5B and sixth vertical transfer pulse Vφ6 are fed continuously to the vertical registers, and a series of the first horizontal transfer pulses Hφ1A, Hφ1B, and second horizontal transfer pulses Hφ2A, Hφ2B are fed intermittently to the solid-state image sensing device every one vertical period. This causes the electric charges accumulated in the pixels to be transferred as described later.
When the shutter button is depressed, in a first vertical period (#1V), a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed. Next in a second vertical period (#2V), electric charges accumulated in the pixels due to the exposure in the first vertical period are transferred, and then, based on an image signal thereby obtained, a calculation for an exposure time and a focus adjustment value is performed. Then the exposure time and focus adjustment value obtained by the calculation are set. In addition, a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed.
Subsequently in a third vertical period (#3V), electric charges accumulated in the pixels due to the exposure in the second vertical period are transferred, and then, based on an image signal thereby obtained, a calculation for an exposure time and a focus adjustment value is performed. Then the exposure time and focus adjustment value obtained by the calculation are set. In addition, a series of subpulses φSUB are fed to the solid-state image sensing device to sweep out electric charges accumulated in the pixels, and thereafter the imaging area is exposed. At this time, the exposure time and focus adjustment value set in the third vertical period will be reflected. Similarly, the following exposure, transfer, calculation and setting are concurrently performed during one vertical period.
When the shutter button is depressed, the above conventional digital still camera with a calculation time less than one vertical period performs a series of photographing operations of an exposure, a transfer, calculation and setting over two vertical periods and every one vertical period as described above, and starts a photographing operation for image recording at a time point when an optimum exposure time and focus adjustment value are obtained.
There has been proposed a solid-state image sensing device driving timing generator that subtracts an exposure time from a horizontal line number per one field to calculate a pulse number of a charge sweep signal XSUB, and outputs the charge sweep signal XSUB with the calculated pulse number (see JP 10-136271, A). There has been also proposed a solid-state image sensing device that sets the number of electronic shutter pulses φSUB when a frame read mode is set so that exposure times in respective fields are the same (see JP 2001-268452, A).
However, the conventional digital still cameras have been suffering from a problem of increased power consumption because a series of photographing operations are performed every one vertical period as shown in FIG. 8 and FIG. 9, so that the subpulse φSUB is fed to the solid-state image sensing device to perform an exposure operation, and the vertical transfer pulses Vφ1-Vφ6 and horizontal transfer pulses Hφ1A, Hφ1B, Hφ2A, Hφ2B are fed to the solid-state image sensing device to perform a transfer operation, throughout the whole period during which the series of photographing operations are repeated.